Generally speaking, in order to establish a communication session between two or more nodes over a network, a setup signaling process will occur. The entities involved in the setup signaling process, and the particular steps of the process, may depend on various factors, such as the capabilities of the nodes and the arrangement of the network.
In some scenarios, participating nodes may exchange setup signaling messages with each other. For instance, if both nodes sit on a packet-switched network such as the Internet and are compliant with the well known Session Initiation Protocol (SIP), one node (the “originating” node) might send a SIP “INVITE” message to the other node (the “terminating” node), specifying a type of session desired. The terminating node may then respond with a SIP “200 OK” message, agreeing to participate, and the originating node may then send a SIP “ACK” to the terminating node, to complete the setup signaling. The originating and terminating nodes may then start engaging in the specified type of session with each other.
In other scenarios, either or each node might be served by a signaling proxy, such as a gateway (e.g., network access server) or switch, which can function to engage in setup signaling on behalf of the node. An example of this occurs in a telephone system, in which each telephone or other telephony device at the end of a call is served by a network switch or gateway, and the switches or gateways are coupled together by a transport network such as the public switched telephone network (PSTN) or the Internet. In particular, an originating phone may be served by an originating switch/gateway, and a terminating phone may be served by a terminating switch/gateway. (Alternatively, the two ends may be served by a common switch/gateway.)
In this arrangement, when a user of the originating phone places a call to the terminating phone, the originating phone may send tones representing the dialed phone number to the originating switch/gateway, and the originating switch/gateway may then respond by sending a call setup message to the terminating switch/gateway. The call setup message may take various forms, depending on the form of the transport network. For example, if the switches/gateways are coupled together by a circuit-switched network such as the PSTN, then the call setup message might be an industry standard “ISUP” Initial Address Message (IAM), which might pass through an out-of-band signaling system between the switches/gateways. As another example, if the switches/gateways are coupled together by a packet-switched network such as the Internet, then the call setup message might be a SIP INVITE or other such session setup message.
Upon receipt of setup message, the terminating switch/gateway would then send an alert signal such as a ring signal to the terminating phone, in response to which a user of the terminating phone (or the phone itself) may take the terminating phone off hook. When the terminating switch/gateway detects the off hook condition, it responsively sends a positive acknowledgement signal to the originating switch/gateway. And the originating switch/gateway then routes the call over the transport network to the terminating switch/gateway. With a call path thus established between the originating and terminating phones, the call may then begin.
In an alternative arrangement, by way of example, it is possible that only one of the phones may be served by a gateway/switch, in which case one phone may directly engage in setup signaling with the other phone's gateway/switch. For instance, if the originating phone includes a SIP client, the originating phone may send a SIP INVITE over a packet-switched network to the terminating switch/gateway, seeking to set up a call with the terminating phone. The terminating switch/gateway would then page the terminating phone, and, when the terminating phone goes off hook, the terminating switch/gateway would positively respond to the originating phone. After completing the setup signaling, the call could then begin.
It is also possible that more than two nodes may be involved in the setup process. For instance, an originating node may seek to set up a conference session with multiple terminating nodes. To do so, either the originating node or a conference server (or switch/gateway) acting on behalf of the originating node might send session setup messages to each of the terminating nodes, or to switches/gateways serving the terminating nodes. Session legs could then be established between the various nodes, and those legs could be bridged together to establish a conference.
In general, regardless of whether a terminating node is served by a proxy, the process of setting up a communication session will typically involve exchanging setup signaling with the terminating node in order to determine whether the terminating node will participate in the session. In particular, a session invitation of some sort (e.g., a SIP INVITE, or a ring signal) will be sent to the terminating node. If the terminating node agrees to participate in the session, the terminating node will then positively acknowledge the invitation (e.g., by going off hook or by sending a SIP 200 OK).
The process can work perfectly well in a scenario where the terminating node has an available link with the network over which to exchange such messages. However, a significant delay in the setup process can occur if the terminating node does not have such a link when the network seeks to send a session invitation to the terminating node. In that scenario, the terminating node must first acquire the link in order to engage in setup signaling.
An example of this delay can occur in a cellular wireless communication system, where a wireless client station can have a “dormant” mode in which it lacks a radio link over which it can physically communicate.
In a “3G” cellular wireless system, for instance, a mobile station may lose its radio link and thus enter a dormant mode after a certain period of time during which no data flows between the mobile station and a base station. When the base station thereafter receives packet data that is being transmitted to an IP address of the mobile station, the base station may need to re-establish the mobile station's radio link. To do so, the base station would page the mobile station over a radio control channel, and the mobile station would responsively request use of a radio traffic channel. In response, the base station would instruct the mobile station to operate on a particular traffic channel, and the base station may then transmit the packet data over that traffic channel to the mobile station.
In a typical 3G wireless system, this process of waking up a terminating mobile station to deliver incoming packet data can sometimes take over 5 seconds to complete, at least in part because the mobile station may only periodically monitor the control channel for page messages. If the incoming packet data represents a session invitation, such as a SIP INVITE for instance, such a delay in setting up the requested communication session can sometimes be problematic. Therefore, an improvement is desired.